After you clean everything it's a good idea to carefully rinse the areas where you've cleaned. You want to be as gentle as you can. Here's how I did it.
Dave
https://youtu.be/kbOyOf4A8EM
This is exactly how interior of my C337B is currently, it's all gutted and I even took more out of it to it's bare bones. There are no instruments or radios , yokes in the cockpit, just wires, cables, couple old heat ducting hoses, mechanisms for yokes and trimming dials. All my floor panels will be replaced as they all are corroded but it looks as inside the belly is still pretty good yet full of dirt n grime from sitting out in elements for last 12-15 years..
AP-AVM